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## [TowerTalk] Multiple-layer stress modulus???

 To: [TowerTalk] Multiple-layer stress modulus??? W8MM@ibm.net (Mike Valentine - W8MM) Wed, 07 May 1997 23:42:52 +0100
 ```Chad Kurszewski WE9V wrote: > > >That got me thinking that my assumtions might be out in left field. > > > >For 2"O.D./1.5"I.D. -> pi((2*4)-(1.5*4))/32(2) = 0.537 in*3 > > > > > >For 2"O.D./1.75"I.D. -> pi((2*4)-(1.75*4))/32(2) = 0.325 in*3 > > 1.75"O.D./1.5"I.D. -> pi((1.75*4)-(1.5*4))/32(1.75) = 0.242 in*3 > > > > Sum of modulii = 0.325 + 0.242 = 0.567 > > > >0.567/0.537 -> 5.6% improvement from taking it in two layers??? > > > >Weird, eh? What am I doing wrong here?? > > Mike, > > I don't think that you can add the modulii like that. > The correct way (from QHS book) is the total OD and the total ID. > > I'm not sure of the reason. > > --- > Chad Kurszewski, WE9V e-mail: Chad_Kurszewski@csg.mot.com > The Official "Sultans of Shwing" Web Site: http://www.QTH.com/sos Hi Chad, thanks for the reply. I looked thru Dave's book as closely as I could muster and didn't see the reference; and I was looking there for it! I asked an M.E. (I'm an E.E.) at work who used to build hi-performance bicycle frames, and he thought one just added them. When I showed him my example, he thought that it was approximately correct and the differences were probably due to the formula being a short-cut from the integrals that tell the real story and that 5% was maybe due to some dropped polynomial terms that didn't show up in the formula for sake of simplicity. What page is your reference? Thanks again for taking the time. Mike - W8MM - EM79sd -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
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